Abstract
Sustainable barley (Hordeum vulgare L.) production will require access to diverse ex-situ conserved collections to develop varieties with high yields and capable of overcoming the challenges imposed by major abiotic and biotic stresses. This study aimed at searching efficient approaches for the identification of new sources of resistance to barley leaf rust (Puccinia hordei Otth). Two subsets, Generation Challenge Program Reference set (GCP) with 188 accessions and leaf rust subset constructed using the filtering approach of the Focused Identification of Germplasm Strategy (FIGS) with 86 accessions, were evaluated for the seedling as well as the adult plant stage resistance (APR) using two barley leaf rust (LR) isolates (ISO-SAT and ISO-MRC) and in four environments in Morocco, respectively. Both subsets yielded a high percent of accessions with a moderately resistant (MR) reaction to the two LR isolates at the seedling stage. For APR, more than 50% of the accessions showed resistant reactions in SAT2018 and GCH2018, while this rate was less than 20% in SAT2017 and SAT2019. Statistical analysis using chi-square test of independence revealed the dependency of LR reaction on subsets at the seedling (ISO-MRC), as well as at the APR (SAT2017 and SAT2018) stage. At seedling stage, the test of goodness of fit showed that GCP subset yielded higher percentages of resistant accessions than FIGS-LR in case of ISO-MRC isolate but the two subsets did not differ for ISO-SAT. At APR, FIGS approach performed better than GCP in yielding higher percentages of accessions in case of SAT2017 and SAT2018. Although some of the tested machine learning models had moderate to high accuracies, none of them was able to find a strong and significant relationship between the reaction to LR and the environmental conditions showing the needs for more fine tuning of approaches for efficient mining of genetic resources using machine learning.
Highlights
Cultivated barley (Hordeum vulgare subsp. vulgare L.) is the fourth most important cereal crop in the world after wheat, maize, and rice, in terms of production of 143.13 million metric tons and acreage of around 47.37 million hectares (FAOSTAT 2017)
A total of 188 accessions from the reference set constructed within the Generation Challenge Program (GCP) and extracted from the composite set of barley collection held at ICARDA based on diversity of EST-derived and genomic SSR markers (Supplementary Table S1)
More resistant accessions were noted when tested to ISO-MRC isolate with 5.88% for FIGS_LR and 22.75% for GCP compared with ISOSAT isolate that showed 10.47% and 13.3% resistant accessions for FIGS_LR and GCP, respectively
Summary
Cultivated barley (Hordeum vulgare subsp. vulgare L.) is the fourth most important cereal crop in the world after wheat, maize, and rice, in terms of production of 143.13 million metric tons and acreage of around 47.37 million hectares (FAOSTAT 2017). The lower national average grain yield of barley is due to limited or no use of inputs, and the prevalence of abiotic and biotic constraints Maculata), spot blotch (Cochliobolus sativus), and leaf rust (Puccinia hordei) are important biotic constraints that limit the grain and straw yields and their quality. Barley leaf rust caused by Puccinia hordei Otth (Ph) is one of the most destructive and globally spread barley diseases (Clifford 1985; Park et al 2015) It is widely distributed throughout barley growing region, and can cause serious yield losses in the regions of North Africa, Europe, New Zealand, Australia, the Eastern and Midwestern parts of United States, and some parts of Asia, where susceptible and late maturing varieties of barley are sown (Arnst et al 1979; Clifford 1985; Chicaiza et al 1996; Brunner et al 2000; Niks et al 2000).
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